8 M Loomis — Results derived fror 



i of the 



A considerable part of the remaining rise may probably be 

 ascribed to the accumulated effect of the sun's radiation for 

 many successive days without the interference of northerly 

 winds. As early as the 10th of June there was a large rise of 

 the thermometer at Fort Benton and Virginia City° aod this 

 was maintained pretty steadily until the 17th. This heated air 

 drifted slowly to the eastward and on the 18th reached the 

 neighborhood of the Great Lakes. 



urnal oscillation of temperature observed at Den- 

 sity, probably depends somewhat upon the config- 

 uianuu ui nie surrounding country, but the most important cir- 

 cumstance is the extreme dryness of the climate of this region. 

 In a country where the annual rain-fall is small, and the sur- 

 face of the earth becomes very dry, the earth readily absorbs 

 the rays of suu, and there is little evaporation to eoanteracl I beir 

 heating effect. The thermometer therefore du: 



-lair than it would if the earth were m 



with green grass. At night, on the contrary, the heat is rap- 

 idly dissipated, and there is no vapor to be condensed, which 

 by thejatent heat liberated would counteract the effects of radia- 

 "™ i during the night the thermometer sinks lower than 

 a moist atmosphere. 

 The same phenomenon is noticed in other countries which 

 have a dry climate. At Madrid in Spain the mean diurnal 

 oscillation of the thermometer is much greater than in most 

 parts of Europe. The following table shows the difference be- 

 tween the mean of the daily ma: minima at 

 Madrid for the months of June and July during a period of eight 

 years. The fourth column shows the highest temperature 

 year, and the fifth colui 





t would i 





i-fall of e 





Range of thermometer at 



Madn 



/, S/Hliil 



Height, 193 



\feet. 



»— 



*».. 





H^t^p. 



l 



"° fa "" 



1868 



25°-2 Fahr. 



31-5 



I V. 





101°1 F. 



1871 

 1872 



27-9 



|f 







l 



If 



I 



Mean 



29-7 



318 



1042 



u 



; > 



The ] ast column in the table on page 6 shows 

 1873, an unusual drought prevailed thromrho 

 Wyoming and Montana. In consequence of this 



